I. Field of the Invention
The present invention relates to a cold start fuel control system for an internal combustion engine.
II. Description of Related Art
Most modern day internal combustion engines of the type used in automotive vehicles include a plurality of internal combustion chambers. A primary intake manifold has one end open to ambient air and its other end open to the combustion chambers via the engine intake valves. During a warm engine condition, a multipoint fuel injector is associated with each of the internal combustion chambers and provides fuel to the internal combustion chambers. The activation of the fuel injectors is typically controlled by an electronic control unit.
During a cold start engine condition, however, a single cold start fuel injector is oftentimes used to provide fuel to the air intake of the primary manifold to the engine in lieu of the main fuel injectors. The cold start fuel injector injects a sufficient fuel/air mixture into the intake of the primary intake manifold to provide fuel for the engine combustion chambers during an engine warm up period. As the engine warms up, the cold start fuel injector is gradually deactivated while, simultaneously, the multipoint fuel injectors are gradually activated in order to provide a smooth transition between a cold engine condition and a warm engine condition.
In order to ensure engine start up during a cold engine condition, these previously known cold start fuel control systems typically inject sufficient fuel to the engine to achieve a rich fuel/air mixture typically having a ratio in the range of 1:10 to 1:14. While such a rich fuel/air mixture is sufficient to ensure proper starting of the engine during a cold engine condition, it disadvantageously results in undesirable hydrocarbon and nitrous oxide emissions.
In an effort to minimize or at least reduce such undesirable emissions, many previously known cold start fuel control systems have utilized heaters to vaporize the fuel prior to the induction of the fuel/air mixture into the inlet end of the primary intake manifold. However, since the fuel/air mixture from the cold start fuel injector must pass entirely through the primary intake manifold of the engine, fuel condensation can occur within the intake manifold during a cold engine condition. Such fuel condensation adversely affects the fuel efficiency of the engine.
Furthermore, with these previously known cold start fuel control systems, since the fuel/air mixture from the cold start fuel injector must travel entirely through the relatively large volume primary intake manifold before the fuel/air mixture reaches the internal combustion chambers, an appreciable time delay occurs between the activation of the cold start fuel injector and the time that the fuel/air mixture reaches the engine combustion chambers. This time delay necessitates excessive engine cranking and also results in slow engine starting.